1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device and a display device.
In this specification, a semiconductor device means all types of devices which can function by utilizing semiconductor characteristics, and a display device, an electro-optical device, a photoelectric conversion device, a semiconductor circuit, and an electronic device are all semiconductor devices.
2. Description of the Related Art
As a type of field-effect transistor, a thin film transistor whose channel region is formed using a semiconductor film that is formed over a substrate having an insulating surface is known. There are techniques in which amorphous silicon, microcrystalline silicon, or polycrystalline silicon is used for the semiconductor film which is used for the channel region of the thin film transistor. A typical application of the thin film transistor is a liquid crystal television device, and the thin film transistor has been put to the practical use as a switching transistor in each pixel included in a display screen.
Further, a technique in which an inverted staggered thin film transistor is used as a switching transistor in a pixel in order to manufacture a large-size television device with high productivity is disclosed (see Patent Document 1). A thin film transistor with high on-state current is needed to manufacture a liquid crystal display device having high definition (a large number of pixels) (e.g., a full high-definition (FHD) liquid crystal display device, a liquid crystal display device with 4K2K resolution, or a liquid crystal display device with 8K4K resolution). Accordingly, a thin film transistor whose channel region is formed using a microcrystalline silicon film, which has higher on-state current than a thin film transistor whose channel region is formed using an amorphous semiconductor film, has attracted attention as a switching transistor in a pixel.